Method of sterilizing plaster of paris surgical dressings



United States Patent METHOD OF STERILIZING PLASTER OF PARIS SURGICAL DRESSINGS Armand M. Marinaro, Wildwood Crest, and Leo Brickman, Metuchen, N. J., Jane E. Smith Holden, Fort Bragg, N. C., and Mary Anne D. Vickery, New Brunswick, N. J., assignors to Johnson & Johnson, a corporation of New Jersey No Drawing. Application November 15, 1954 Serial No. 468,994

8 Claims. (Cl. 21-57) This invention relates to sterilization of plaster of Paris bandages.

Plaster of Paris is the hemihydrate of calcium sulphate and is commercially prepared by heating gypsum (Ca SO .2H O) to remove a portion of the Water of crystallization to form the hemihydrate plaster of Paris (Ca SO M2H O). When the plaster of Paris is mixed with water, the hemihydrate rehyclrates to gypsum and forms a hard solid mass or cast. This phenomenon is known as setting plaster of Paris, and time taken to form the cast is known as the setting time of plaster.

Extensive use of these properties of plaster of Paris is made in orthopedic bandages. The bandage comprises particles of plaster of Paris adhered to crinoline or other type of backing material. In use, the bandage is dipped in water for a short time by the physician or surgeon, squeezed to express excess water and then wrapped around the portion of the body of the patient and allowed to set up as a cast. Plaster or" Paris orthopedic bandages should have a fast setting time for this enables the doctorto shorten the time that the patient must be held in traction while the plaster hardens. Furthermore, a cast thus formed should have good high initial cast strength so that when the patient is removed from the operating or cast room, the cast will not break down and the member will remain immobilized.

Requirements of the medical profession with respect to quality of surgical dressings have become more stringent and exacting the past few years. Accordingly, efforts have been made to sterilize plaster of Paris bandages just as most other surgical dressings are sterilized before use. In conventional methods of sterilization, live wet steam under pressure, or several treatments of boiling water, are

usually employed. In these cases it becomes extremely difiicult, if not impossible, to prevent contact or condensation of moisture on the plaster, as a result of which the useful qualities of the bandage, by reason of the properties of plaster of Paris, enumerated above, are impaired or destroyed. For example, as a plaster of Paris bandage is autoclaved in the conventional manner with 15 to 20 lbs. steam gauge pressure for 30 minutes, the bandage, upon removal from the autoclave, is found to be greatly retarded in setting time beyond the period which would be found to be useful by the orthopedic surgeon. A bandage so treated, which may have an original setting time of 5 to 8 minutes, after treatment in the autoclave does not set within an hour, if at all.

Objects of the present invention include provision of a process for sterilizing plaster of Paris bandages without impairing the qualities of setting time and cast strength upon which the usefulness of plaster of Paris in orthopedic work depends.

A further object of the invention is to sterilize the plaster of Paris bandage in such a manner that the bandage, properly handled, will retain its sterility indefinitely.

According to the invention, plaster of Paris bandages are sterilized by sealing them in a container impermeable to water vapor and microorganisms, andheating them in.

the container in the presence of an amount of water controlled below a certain maximum level, at temperatures set forth below and time to bring about sterilization. A particular embodiment of the invention is directed to additional use of a certain chemical sterilizing agent, in which case water vapor content and temperature may be advantageously maintained at certain lower levels.

The presence of water in the sterilization container is necessary to kill all the microorganisms. According to the invention, sterility is produced without resultant degradation of the plaster of Paris due to water by controlling the amount of water present in the system at a value not greater than 1.1 parts by weight per parts of the weight of the plaster of Paris. When, in addition to the water, certain amounts of chemical sterilizing agent are added according to an embodiment of the invention hereinafter described, water content may advantageously be maintained at a level not greater than 0.55 part per 100 parts by weightof plaster of Paris. The minimum amount of water to produce sterility will vary from 0.13 part per 100 parts by weight of plaster of Paris when chemical sterilizing agent is utilized, to 0.5 part when there is no chemical sterilizing agent present. Accordingly, generally speaking, the minimum amount of water present will be at least 0.13 part, and suflicient to sterilize. The necessary amount of water may be introduced by means of a hydrated salt which may liberate water of crystallization at the elevated temperatures used for sterilization. Examples of salts of this nature are gypsum, Epsom salts, washing soda, .etc. The amountsof such a salt utilized are those equivalent to the amounts of water set forth above. The water or water-yielding salt is added to the sterilizing container in such a manner as not to come into direct contact with the plaster of Paris.

Another variable in the process is temperature, which is sufiiciently high so that under the conditions maintained, sterility will result. Without the assistance of a chemical sterilizing agent, temperatures at or above about 240 F. may be found necessary to sterilize within a reasonable time. With a chemical sterilizing agent, temperatures above about 212 F. may be found effective. Hence, generally speaking, satisfactory temperatures are those at or above 212 F. at which the system may be sterilized under the conditions maintained therein. Temperatures as high as 290 F. may be used, but abovethis level some discoloration and deterioration of the bandage, and, in particular, the backing material for the bandage, may take place. The temperature is maintained at a level, and the sterilizing conditions prevail, for sufficient time to kill all microorganisms, a balance being chosen between shorter sterilization times in the range of oneof plaster of Paris, the minimum amounts of water and.

the minimum temperature levels being those outlined above, i. e. at least about 212 F. and 0.13 part of water per 100 parts by weight of plaster. A scavenger may be added to the sterilizing container to destroy residual formaldehyde. Such a material is, for example, urethane.

The following examples, demonstrating the manner in which the invention methodis carried out, are presented as illustrating rather than limiting the invention.

Example I 4" by yd. commercially available plaster of Paris orthopedic bandage rolls were in all cases utilized. A. strip of gauze inoculated with highly resistant sporebearing organisms was added to each bandage roll. All materials were dried at 45 C. for 16 hours'beforehand in order to remove all traces of free moisture. The bandage was placed in a steel container to which there had already been added a predetermined amount of water or water-yielding salt. A grid or stand had been placed on thebottom of the container to prevent the bandage frorncoming into contact with the water or water-yielding salt and absorbing or reacting therewith. The con- 4 maximum level, or a chemical sterilizing agent plus certain smaller amounts of water, while maintaining sterilizing temperatures for time suflicient to produce the desired effect.

The invention has been described in connection with one embodiment only, but many modifications and equivalents thereof are included within its scope.

The claims are:

1. The method of sterilizing plaster of Paris which comprises treating said plaster of Paris in an enclosed space with water vapor in an amount in the range of about 0.13 to 1.1 parts by weight per 100 parts of plaster of Paris, :1 formaldehyde providing material in an amount to provide under the treating conditions an amount of formaldetainer was sealed and then heated in a hot air oven at g the range of h 0 9 Pai't a predetermined time and at a predetermined oven tem- 1 0 parfts 2 51 a t.emp.era;ure m t 2 perature. After allowing the bandage tocool for 24 range 0 3 out to e hours, each of the bandages was tested for setting time 9 to 3 WherePy a itenhzed plaster of Pans and cast strength as described in Federal Specification 2O g sg having settmg time not over about 22 GG-B-107, paragraphs 4.3.5. and 4.3.6. Sterility testa ing was carried out according to USP XIV. Theresults a The mgthod f n I i i a.plaster of Pal-' are Summarized in the following table ban age enclosed in a container which is nonporous t0 micro-organisms.

I Steriliz- Setting 1 hour Test Water Added (Parts Temp, tng Time, Cast Sterility per 100 of Bandage) 1 F. Time, min. Strength,

hrs. lbs.

0 265 2 6% 460 N ot sterile. n. 265 2 6 420 Do. 0. 265 2 6% 440 Do. 0. 265 2 6 410 Sterile. 0. 265 2 Not sterile. 0. 265 2% 14 402 Sterile. 0. 290 2 13 364 Do. 0. 255 2 11 417 Do. 0. 265 2 342 Do. 0 Water+3.85 285 2 11% 337 Do.

ypsum. Untreated Controls. 7% 462 Not sterile.

1 Bandages were plaster of Paris, 10% fabric. by weight.

Example [I 3. The method of claim 2 wherein the amount of form- VThe Procedure outlined in Example I was repeated, aldehyde is about 0.13 part and the heatingv is under except that a formaldehyde-yielding material and, in some e Y s 1 h 9., cases, a formaldehyde scavenger (urethane), was also T 8 met 0d of Cam 3 w erem the contamer 1S incorporated in the sterilizing container. After the heat nonporous to Water treatment the bandages were allowed m cool f 24 hours, 4.5 5. The method of claim 4 wherein water is introduced and tested for sterility, setting time and cast strength acas hquld: and the bandage 13 Supported the contamer cording to the procedures presented in Example 1, R to avoid direct contact between'the liquid water and the suits are presented in the following table: Plaster 0f Pans- Steriliz- Temper- Setting 1 hour Test Additives (Parts per of Bandage} 1 ing ature, Time, Cast Sterility Time, F. min. Strength,

hrs. lbs.

0.13 paraformaldehyde 2 212 4% 405 Not sterile. 0.22 paraformaldehyde. 2 212 5 385 D0. 0.67 urethane a 212 4 392 Do. 0.67 methane, 0.22 water 3 212 6% 360 Do. 0.67 urethane, 0.22 paraiormaldehyde 3 212 5% 350 Do. 0.13 paraformaldehyde, 0.22 water... 2 212 6% 374 Do. 0.22 paraiormaldehyde,0.22water 2 212 5% 381 Sterile.

0.045 water, 0.22 paratormeldehyde, 3 212 3% 335 Not sterile.

0.67 urethane. 0.13 water, 0.22 paraformaldehyde, 3 212 6% 365 Sterile.

0.67 urethane. I 0.22 water, 0.22 parai'orm'aldehyde, 3 212 6% 370 Do.

0.67 methane. 0.22 paraformuldehyde, 0.67 urethane, 3 212 6% 352 Do.

1.55 gypsum. 0.5 water, 0.22 paraformaldehyde, 3 212 10% 397 D0.

0.67 methane. 10 water, 0.22 paraformaldehyde, 3 212 12% 397 D0.

0.67 methane. 2.0 water, 0.22 paraiormaldehyde, 3 212 22% 360 Do.

0.67 urethane.

1 Bandages were 90% plaster of Paris, 10% fabric, by weight.

The foregoing examples show that plaster of Paris bandages may be eifectively sterilized consistent with little or no physical or chemical degradation. by treatment with an amount of water vaporv below a certain 6. The method of claim 5 wherein. the. amount of:water is up to about 0.55 part.

7. The method of claim 6 wherein. the-temperature is 75 at least 240 F. and urethane is included in an amountof 5 6 about 0.67 part per 100 parts of plaster of Paris. 1,111,055 Carveth Sept. 22, 1914 8. The method of claim 2 wherein the amount of Water 1,837,264 Hackley Dec. 22, 1931 is at least about 0.5 part and the temperature is at least 2,009,597 Weber July 30, 1935 about 240 F. 2,344,536 Coey et a1. Mar. 21, 1944 5 2,376,611 Miner May 22, 1945 References Cited 111 the file 0f th1s Patent 2 472 011 Graham May 31 1949 UNITED STATES PATENTS 2,477,964 Corblin Aug. 2, 1949 830,831 Gronwald Sept. 11, 1906 855,942 Duret June 4, 1907 10 FOREIGN PATENTS 510,273 Great Britain July 31, 1939 

1. THE METHOD OF STERILIZING PLASTER OF PARIS WHICH COMPRISES TREATING SAID PLASTER OF PARIS IN AN ENCLOSED SPACE WITH WATER VAPOR IN AN AMOUNT IN THE RANGE OF ABOUT 0.13 TO 1.1 PARTS BY WEIGHT PER 100 PARTS OF PLASTER OF PARIS, A FORMALDEHYDE PROVIDING MATERIAL IN AN AMOUNT TO PROVIDE UNDER THE TREATING CONDITIONS AN AMOUNT OF FORMALDEHYDE IN THE RANGE OF ABOUT 0 TO ABOUT 0.13 PART PER 100 PARTS OF PLASTER OF PARIS, AT A TEMPERATURE IN THE RANGE OF ABOUT 212 TO 290*F., FOR A TIME IN THE RANGE OF ABOUT 1 TO 3 HOURS, WHEREBY A STERILIZED PLASTER OF PARIS IS OBTAINED HAVING A SETTING TIME NOT OVER ABOUT 22 MINUTES. 